This invention relates to improved lubrication in internal combustion engines and, more particularly, to improving lubrication characteristics at exhaust ports in such engines.
Prior art of possible relevance includes U.S. Pat. No. 3,448,727 issued June 10, 1969 to Kobayakawa.
The use of bridging elements at exhaust ports in both reciprocating and rotary engines for supporting compression seals carried by reciprocating and rotary pistons for the purpose of reducing the unsupported span of the seal is highly desirable. However, the environment at such bridging is not at all conducive to the formation and maintenance of adequate oil films for lubricating the seals. Typically, the seals operate in the region of very thin oil film thickness known as elasto-hydrodynamic film lubrication or even boundary film lubrication. Thus, notwithstanding the use of expensive and sophisticated materials in the formation of the housings and seals in such mechanisms, the wear rate is frequently quite high.
At the bridging in engines, the exhaust gas termperatures are quite high and the bridging does not have a cooling down period during the induction stroke of the engine of any significant duration. Moreover, contact stresses with the seals are high because of the inevitable so-called "jumping" movement that the seal undergoes as it passes the port moving in and out of the same.
Heretofore, it has been thought impossible to cool the bridging adequately in such a way as to increase the thickness of the oil film and improve the maintenance of the same by reason of the bulk required to place cooling passes in such bridging, which is contradictory to good porting. In other words, the increased width of the bridging required to provide cooling passages therein interferes with good breathing characteristics of the engine, thereby reducing the efficiency of its operation.